Epidemiological and clinical features of Minamata disease

Minamata disease is methyl mercury intoxication from fish contaminated by a chemical factory in Minamata city. Based on the results of our regional survey, cardinal clinical features of the disease were clarified by a multivariant analysis of all symptoms in inhabitants in the polluted area. The clinical features were found to be essentially the same as those of Hunter Russell syndrome; however, some additional symptoms were also found. Those symptoms are influenced by many factors, such as degree of exposure and duration of pollution. The disposition of each inhabitant also plays a role in clinical manifestation. This analysis contributes to a correct individual diagnosis and to the correct estimation of patients in polluted areas. Long-term studies also uncovered a few inhabitants who claimed to have begun to experience some neurological symptoms after pollution ceased. These symptoms were attributed mainly to aging. As many inhabitants with mild neurological complaints were not easily diagnosed, a questionable borderline group should be postulated for social settlement of Minamata disease. The characteristics of Minamata disease are discussed and compared to cases of methyl mercury poisoning in other parts of the world.